H. David Politzer, Asymptotic Freedom, and Strong Interaction

H. David Politzer has won the
2004 Nobel Prize in Physics ‘for the discovery of asymptotic
freedom in the theory of the strong interaction'. ‘Politzer, a
professor of theoretical physics at the California
Institute of Technology, shares the prize with David Gross and Frank
Wilczek.
The key discovery celebrated by [the] prize was made in
1973, when Politzer, a Harvard University graduate student at the time,
and two physicists working independently from Politzer at Princeton University–Gross and his graduate student
Wilczek–theorized that quarks actually become bound more tightly
the farther they get from each other.

This discovery has been known for 31 years as "asymptotic freedom,"
and is often described by physics professors to their students with
the analogy of a rubber band increasing in tightness as it is pulled
apart. Asymptotic freedom established quantum chromodynamics (QCD) as
the correct theory of the strong force, one of the four fundamental
forces of nature.'

"The following information [from The
Discovery of Asymptotic Freedom] was written by Caltech's MacArthur
Professor of Theoretical Physics John Preskill, a colleague of
Politzer's.
Preskill prepared the text upon learning that Politzer had won the
Nobel Prize ...:

Of the four fundamental forces–the others besides the strong
nuclear force are electromagnetism, the weak nuclear force (responsible
for the decay of radioactive nuclei), and gravitation–the strong
force was by far the most poorly understood in the early 1970s. It had
been suggested in 1964 by Caltech physicist Murray Gell-Mann that protons
and neutrons contain more elementary objects, which he called quarks.

Yet isolated quarks are never seen, indicating that the quarks are
permanently bound together by powerful nuclear forces. Meanwhile, studies
of high-energy collisions between electrons and protons performed at
the Stanford Linear Accelerator
Center (SLAC) had probed the internal structure of the proton, and
Caltech's Richard Feynman had suggested in 1969 that the results of
these experiments could be explained if quarks inside a proton are nearly
free, not subject to any force. Feynman's suggestion, together with
the observation that quarks are unable to escape from nuclear particles,
posed a deep puzzle: how could nuclear forces be both strong enough
to account for the permanent confinement of quarks and weak enough to
account for the SLAC experiments?

The discovery of asymptotic freedom provided a highly satisfying resolution
of this puzzle. The calculations of Gross, Wilczek, and Politzer showed
that in quantum chromodynamics (QCD), quarks are held together strongly
when separated by a distance comparable to the size of a proton, explaining
quark confinement. Yet for the smaller separations explored in the high-energy
SLAC experiments, the attraction is weaker, supporting Feynman's proposal."